Constraining the Variability in Ages, Sources and Reactivity of Organic Matter Transported by Rivers of the Northeast U.S. to the Ocean Margin
Abstract
Riverine transport of organic carbon (OC) is a significant flux in the global C budget, representing major terms for both terrestrial losses and ocean margin inputs. Rivers are also dynamic systems where the chemical and isotopic character and reactivity of terrestrial OC is modified prior to its export to the margins. However, several major unknowns still exist in land-ocean OC fluxes, including: i) the amounts, ages and character of the OC reservoirs mobilized and transported; ii) the scales of variability in these parameters both within and among different systems; iii) the extent of modification of these parameters by microbial and abiotic processes during riverine and estuarine transport. The use of natural radiocarbon in aquatic and marine studies provides unique source, turnover and processing information with respect to local, regional and global carbon budgets. However, the number of C-14 analyses in most river systems is often too small, thus limiting the full potential of this isotope in carbon studies. As part of our on-going work, we are measuring the C-14 signatures and ages of dissolved and particulate organic carbon (DOC and POC, respectively), as well as dissolved inorganic carbon (DIC), in a group of northeast U.S. rivers. Here we report the ranges in radiocarbon signatures of bulk DOC, and POC, DIC and their associated 13C/12C ratios from measurements on seven different river systems. The rivers studied occupy a relatively small geographic range, yet individually they export both ancient and fully modern average-aged C to the coastal ocean. In addition, microbial heterotrophy appears to be responsible for the loss of both contemporary and highly aged OC, depending upon the dominant sources to a given system. While sample numbers still preclude an in-depth understanding of the sources and fates of different aged components in river systems in general, the data set permits some preliminary conclusions concerning the relative importance of wetlands, ancient marine organic matter, and within- system modification as key potential controls on riverine C ages.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2004
- Bibcode:
- 2004AGUSM.H12A..04B
- Keywords:
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- 0400 Biogeosciences;
- 1040 Isotopic composition/chemistry;
- 1055 Organic geochemistry;
- 1800 HYDROLOGY